Text using 6-bit ASCII

TABLE 28
International function message 0 using Message 26, broadcast or addressed binary message

Parameter	Number of bits	Description
Message ID	6	Identifier for Message 26; always 26
Repeat indicator	2	Used by the repeater to indicate how many times a message has been repeated. See § 4.6.1, Annex 2; 0-3; 0 = default; 3 = do not repeat any more
Source ID	30	MMSI number of source station
Destination indicator	1	0 = Broadcast (no Destination ID field used) 1 = Addressed (Destination ID uses 30 data bits for MMSI)
Binary data flag	1	Always 0
Destination ID	0/30	Destination ID if used.	If Destination indicator = 0 (Broadcast), no data bits are needed for Destination ID. If Destination indicator = 1, 30 bits are used for Destination ID and spare bits for byte alignment.
Spare	0/2	Spare (if Destination ID used)
DAC	10	International DAC = 1₁₀ = 0000000001₂
FI	6	Function identifier = 0₁₀ = 000000₂
Text sequence number	11	Sequence number to be incremented by the application. All zeros indicates that sequence numbers are not being used
Text string	6-942/972	6-bit ASCII as defined in Table 47, Annex 8. When using this IFM, the number of slots used for transmission should be minimized taking into account Table 29. For Message 26 the maximum is 942 for Addressed or 972 for Broadcast.
Spare bits	Max 7	Not used for data and should be set to zero. The number of bits should be either 1, 3, 5 or 7 to maintain byte boundaries. NOTE 1 – When a 7-bit spare is needed to satisfy the 8-bit byte boundary rule, the 6-bit spare will be interpreted as a valid 6‑bit character (all zeros is the “@” character). This is the case when the number of characters is: 3, 7, 11, 15, 19, 23, 27, etc.
Communication state selector	1	0 = SOTDMA communication state follows 1 = ITDMA communication state follows
Communication state	19	SOTDMA communication state (see § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1
Total number of application data bits	128-1 064/ 96-1 064	128-1 064 bits for Addressed, or 96-1064 bits for Broadcast.

Table 29 gives an estimate of the maximum number of 6-bit-ASCII characters that can be in the application data field of the binary data parameter of Messages 6, 8, 25 and 26. The number of slots used will be affected by the bit stuffing process.

TABLE 29

Estimated number of slots	Maximum number of 6-bit ASCII characters based upon typical bit stuffing
	Addressed binary Message 6	Broadcast binary Message 8	Message 25		Message 26
	Addressed binary Message 6	Broadcast binary Message 8	Addressed binary	Broadcast binary	Addressed binary	Broadcast binary
1	6	11	6	11	2	7
2	43	48	−	−	40	45
3	80	86	−	−	77	82
4	118	123	−	−	114	120
5	151	156	−	−	150	163
NOTE 1 – The 5-slot value accounts for the worst case bit stuffing condition.